1. Field of the Invention
The present invention relates to an ink jet printing apparatus, an image processing method and an ink jet printing method which form an image on a print medium by ejecting ink from a print head.
2. Description of the Related Art
Ink jet printing apparatus capable of producing color images usually have a plurality of print heads each ejecting one of four different color inks, cyan, magenta, yellow and black (simply referred to as C, M, Y and K). In recent years, to minimize a granular impression that dots in highlight areas give, there is a growing trend toward producing color images by using light inks with lower densities and dark inks with commonly used densities.
In ink jet printing apparatus currently in wide use, the four color inks (C, M, Y and K) or six color inks, which include LC (lighter cyan ink than C) and LM (lighter magenta ink than M) in addition to Y, M, C and K, are used in separate dedicated print heads. It is known that there is an ejection variation among individual print heads due to a structural variation among the print heads caused by the manufacturing process. The current level of this variation is about xc2x110% of a standard ejection volume. The ejection volume variation among print heads means an ejection volume variation among different color inks, which in turn results in variations in density and color of printed images.
Printers are designed to determine a tone of an output image based on a standard ejection volume of each print head. Hence, if the print heads used have ejection volumes that are deviated from the standard volumes, an image formed by these print heads will have a different tone from that of a target image. Because of a rapid advance in color printing technology of the ink jet printing apparatus in recent years, these apparatus produce photograph-like images that are now close in quality to silver salt pictures. In such photograph-like images, the tone is an important factor that determines the image quality. If a target tone fails to be obtained, there is a risk of undesired phenomena showing up, such as a degradation of color reproducibility, a partial loss of gradation (particularly a degradation of gray scale reproducibility caused by a loss of balance between a dark ink and a light ink of the same color, and a loss of a linear gray scale characteristic), and a formation of pseudo-outline, which may result in a significant impairment of image quality.
To solve the problems described above, a commonly used method involves printing a test pattern to check an ejection volume variation, reading the printed test pattern by a scanner, determining a level of the ejection volume based on a scanned signal level, and changing parameters of image processing according to the ejection volume level. With this method, although a degradation of image quality can be avoided, the user needs to print a test pattern and a reading device such as scanner is required, making the system complex and expensive.
Another method is also known in which a test pattern for determining the level of ejection volume is printed to be visually checked by the user who then enters the check result into a host computer through a user interface to correct the tone. This method however has a problem that because it relies on the user""s visual check, the decision may vary depending on the individual user""s ability or a wrong decision may be made. There is also a possibility of input errors. These in turn will degrade image quality.
Still another method, disclosed in Japanese Patent Application Laid-open No. 2001-063058, has been proposed. In this method the host computer obtains information on the print head ejection volumes preset in a memory installed in the printing apparatus and, according to the ejection volume information, changes image processing parameters in a printer driver in the host computer. Since in this method the information on the print head ink ejection volumes is written into the memory before the printing apparatus is shipped, a high quality output image can be obtained at an initial stage of use through the modification of image processing parameters according to the written ejection volumes.
As the operating hours of the printer accumulate, the actual ejection volumes of the print heads may progressively change with elapse of time, a so-called secular change. This is considered due to changes in the size of bubbles in ink that may be caused by burned electrothermal transducers (heaters) in the print heads or by a slight change in the heater film thickness. In such a case, simply modifying the image processing parameters according to the initial ink ejection volumes stored in the memory can hardly keep a high quality output image for a long period of use.
The present invention has been accomplished with a view to overcoming the above-described problems of the conventional art. It is therefore an object of the present invention to provide an ink jet printing apparatus, an ink jet printing method and an image processing method that enable high quality images to be produced from the initial stage of use of the printing apparatus until the end of its service life.
To achieve the above objective, this invention has the following construction. That is, the present invention provides an ink jet printing apparatus for printing an image on a print medium by using a print head, wherein the print head can eject ink supplied from an ink tank, the ink jet printing apparatus comprising: ink consumption detection means for detecting an amount of ink consumed in the ink tank; ejection number detection means for detecting the number of ink ejections from the print head; ink droplet volume calculation means for calculating an ink droplet volume based on the number of ink ejections from the print head detected by the ejection number detection means and the ink consumption detected by the ink consumption detection means; and control means for changing processing associated with a printing operation according to the ink droplet volume calculated by the ink droplet volume calculation means.
Further, the present invention provides an image processing method for processing print data used to print an image on a print medium by using a print head, wherein the print head can eject ink supplied from an ink tank, the image processing method comprising: an ink consumption detection step for detecting an amount of ink consumed in the ink tank; an ejection number detection step for detecting the number of ink ejections from the print head; an ink droplet volume calculation step for calculating an ink droplet volume based on the number of ink ejections from the print head detected by the ejection number detection step and the ink consumption detected by the ink consumption detection step; and a change step for changing image processing performed on the print data according to the ink droplet volume calculated by the ink droplet volume calculation step.
Further, the present invention provides an ink jet printing method for printing an image on a print medium by using a print head, wherein the print head can eject ink supplied from an ink tank, the ink jet printing method comprising: an ink consumption detection step for detecting an amount of ink consumed in the ink tank; an ejection number detection step for detecting the number of ink ejections from the print head; an ink droplet volume calculation step for calculating an ink droplet volume based on the number of ink ejections from the print head detected by the ejection number detection step and the ink consumption detected by the ink consumption detection step; and a control step for changing processing associated with a printing operation according to the ink droplet volume calculated by the ink droplet volume calculation step.
Further, the present invention provides an ink jet printing apparatus for printing an image on a print medium by using a print head, wherein the print head can eject ink supplied from an ink tank, the ink jet printing apparatus comprising: an ink consumption information obtaining means for obtaining information corresponding to an amount of ink consumed in the ink tank; ejection number information obtaining means for obtaining information corresponding to the number of ink ejections from the print head; ink droplet volume information obtaining means for obtaining information corresponding to an ink droplet volume based on the ink ejection number information obtained by the ejection number obtaining means and the ink consumption information obtained by the ink consumption information obtaining means; and control means for changing processing associated with a printing operation according to the ink droplet volume information obtained by the ink droplet volume information obtaining means.
Further, the present invention provides an image processing method for processing print data used to print an image on a print medium by using a print head, wherein the print head can eject ink supplied from an ink tank, the image processing method comprising: an ink consumption information obtaining step for obtaining information corresponding to an amount of ink consumed in the ink tank; an ejection number information obtaining step for obtaining information corresponding to the number of ink ejections from the print head; an ink droplet volume information obtaining step for obtaining information corresponding to an ink droplet volume based on the ink ejection number information obtained by the ejection number obtaining step and the ink consumption information obtained by the ink consumption information obtaining step; and a change step for changing image processing performed on the print data according to the ink droplet volume information obtained by the ink droplet volume information obtaining step.
With this construction, since the ink ejection volume that changes over time is calculated and, based on the calculated result, the data related to the image forming processing is corrected, it is possible to produce high quality images at all times from the initial stage of use of the printing apparatus till the end of its service life.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.